This proposal would carry forward studies of acquired resistance to T. spiralis in a model system using rats. The focus of the inquiry would be on the resistance to T. spiralis that is transferred passively from a specifically immunized mother to her young. The objectives are to evaluate the role(s) of different subclasses of antibody in acquired resistance to infection; to elucidate the mechanism by which invading muscle larvae become entrapped in mucus; to characterize parasite antigens targeted in the immune response; to ascertain the natural history and regulation of protective, antibody secreting B cells; and to assess the effect of weaning on the ability of antibody to passively protect rats against T. spiralis. Polyclonal antibodies and monoclonal antibodies of known subclass and specificity would be further characterized in passive protection experiments. Hybridoma variants producing antibodies with a protective combining site associated with alternative heavy chains would be selected to determine the importance of isotype in defining the antibody's protect function. This question would be further analyzed by enzymatically cleaving the antibody into F(ab)'2 fragments. Additional monoclonal antibodies would be produced in order to confirm our observation that IgG2c antibodies can be highly protective. The interaction of protective antibodies with mucus would be critically examined. The role of mucus would be investigated to determine whether mucin release is triggered by antigen in the presence of antibody; whether it binds to antibody to form an antigen specific trap or if mucus is entirely passive in action and, in fact, not required for rapid expulsion. We would evaluate the potential of antibodies to induce the release of substances which inhibit larval mobility in mucus or to inhibit such mobility directly. Protective monoclonal antibodies would be used to investigate the distribution and function of their target antigen in muscle larvae. The central question is whether the relevant parasite antigen is targeted because it is expressed on the surfaces of larvae or because it is functionally important to the parasite, particularly to its capacity to invade the epithelium. Epitope mapping with protective and non-protective monoclonal antibodies would be conducted to identify and active site(s) on the target antigen. Another objective is to determine the natural history of protective antibody producing cells. Specific B cell reactivity to relevant parasite antigens during infection would be compared in both mucosal and non-mucosal lymphoid tissues. The influence of helper T cells from various tissues on B cell reactivity and isotype expression would be examined. These experiments would address the question of how an antibody response that is dominated by a single isotype develops during a complex infection. Finally we would assess the effects of weaning on the expression of rapid expulsion. In particular we would evaluate the protective potential for adult of monoclonal antibodies which are protective for infant rats. We would investigate the need for ancillary cells as well as IgE antibodies to facilitate expression of rapid expulsion by the adult.